J. M. Martínez-Duart

Dielectric breakdown processes in anodic Ta2O5 and related oxides

The dielectric breakdown properties during the anodic oxidation of valve metals (Ta, Nb, Al, etc.) are reviewed. First, the theories developed for insulating films flanked by metal electrodes are analysed. The major emphasis is placed on the avalanche models since they give the best account of the experimental facts observed with electrolytic contacts, i.e. during the anodization. Some hints to increase the breakdown potential are finally given.

Electrical properties of electroless NiP thin films

Abstract The influence of the pH and temperature of the electroless solution on the electrical characteristics of the deposited NiP thin films has been determined. The phosphorous content of the films increases when the pH of the solution is decreased giving rise to a diminution of the temperature coefficient of the resistance (TCR). Low TCR films (TCR ⩽ 100 ppm °C−1 are obtained for pH = 3.4. In this pH range the deposition rate can be increased by heating the electroless solution to moderate temperatures.

Double anodization experiments in tantalum

Based on our previous model of anodization, a new formula is given for the relation between the breakdown voltage VB during the anodic oxidation of tantalum and the anodization parameters. The formula predicts the well known diminution of VB with the logarithm of the electrolyte concentration. The model also explains the experimentally-observed fact that VB is solely determined by the latter electrolyte in double anodization experiments.

Deposition of diamond and boron nitride films by plasma chemical vapour deposition

Abstract The deposition problems of diamond and cubic boron nitride (c-BN) by chemical vapour deposition techniques are reviewed, with major emphasis on the nucleation and reaction mechanisms. A discussion is made of the main deposition parameters ( i.e. gas mixture, substrate conditioning, plasma discharges etc.) which favour the formation of the cubic phase. Most of the work is devoted to diamond owing to the large progress attained in this material. In fact, the use of diamond as a hard protective coating is now on a commercial scale. By contrast, the preparation of c-BN layers with good characteristics still needs of further research.

Postbreakdown reanodization of tantalum

The scintillation phenomenon in anodic tantalum oxide has been studied by means of the potential rise during the reoxidation of samples which had undergone previous scintillation for a specified time. The information given by these curves, together with measurements of the dielectric properties, X-ray analysis and observation under the scanning electron microscope, allow two different processes to be distinguished during scintillation. The first stage of the scintillation is mainly characterized by a process of attack and partial healing of the oxide film with the formation of pores and microfissures. The second stage of scintillation is dominated by the process of field crystallization which irreversibly degrades the oxides dielectric properties. The influence of the anodization parameters, such as current density and nature and concentration of the electrolyte, on the above processes is also investigated.

Electrical properties of pyrolytic MnO2 layers

MnO2 samples have been prepared by the pyrolytic decomposition of manganese nitrate in different atmospheres: dry air and air saturated with water vapour. The influence of the atmosphere on the kinetics of the manganese nitrate decomposition and on several physical properties of the resulting MnO2, such as density, grain size, crystalline structure, resistivity and activation energy for electrical conduction, has been studied. The dielectric and breakdown properties of Ta-Ta2O5-MnO2 capacitive structures, using MnO2 as a solid electrolyte, are also strongly affected by the atmosphere in which the MnO2 layers are prepared. It has been found that the electrical conductivity of the MnO2 samples is greater when they are formed in a saturated water vapour atmosphere, resulting in substantially improved characteristics for the power losses and scintillation voltage of the corresponding tantalum capacitors.

Dielectric and structural characteristics of Ta2O5 anodic films formed in phosphoric acid electrolytes

The duplex nature of Ta2O5 films formed in H3PO4 electrolytes with different concentrations has been chanyotarired by net weight gain measurements of the films during the anodic oxidation, as well by capacitance and etch-rate measurements of the oxide films. The density and permittivity of each layer of the films formed in different concentrations of the electrolyte have been calculated.

Dielectric characteristics of miniature aluminium electrolytic capacitors under stressed voltage conditions

The effects of applying voltages higher than the nominal voltageVN, for given periods of time, to miniature aluminium electrolytic capacitors has been investigated. The measurements of the current transients, theI–V characteristics, and the a.c. properties indicate that the main effect of subjecting the capacitors to the high voltages is an irreversible change in the capacitor dielectric characteristics as a consequence of a large increase in the resistance of the electrolyte and in the permanent leakage current through the anodic oxide. This current, very noticeable for voltages higher thanVN, is attributed to an electronic conduction mechanism in an avalanche regime. The measured dielectric parameters and their evolution after exposing the capacitors to stressed voltage conditions are interpreted in terms of an extension of McLeans equivalent circuit for an electrolytic capacitor.

Co-sputtered Si−Cr resistive films

Si-Cr films of variable composition between pure silicon and pure chromium have been deposited by co-sputtering on to glass substrates and thermally oxidized silicon wafers. In order to assess the applications of the Si-Cr films to thin film resistors, the electrical characteristics of the films have been determined as a function of composition, thickness, thermal treatments, etc.

Silicon nitride films deposited from SiF4/NH3 gas mixtures

Silicon nitride films have been deposited from SiF4/NH3/H2 gas mixtures. The deposition reaction at high pressure (52 torr), takes place only for temperatures above 800°C. In the temperature range 800–1000°C the reaction is controlled by a surface process. The increase in H2 and SiF4 partial pressures enhances the deposition rate. The SiF4 molecules provide a high concentration of available silicon atoms, while the hydrogen molecules inhibit the etching effect of the free fluorine atoms. Finally, the effect of an r.f. plasma in the chemical vapour deposition reaction has been evaluated.